It has been known that p-menthane-3,8-diol has a repellent effect on insect pests such as the mosquito, slug, millipede, night crawler and flea (see H. Nishimura, J. Mizutani, T. Umino & T. Kurihara, 6th Intern. Congr. Pesticide Chem., Abstracts 2D/E-07, Ottawa, Canada, Aug. 10-15th (1986); H. Nishimura, Eucalyptus as Future Biosource, and Biotechnology and Bioscience Thereof, Uchidarokakuho (1987); H. Nishimura, T. Nakamura & J. Mizutani, Phytochemistry, 23, 2777 (1984); H. Nishimura, Fragrance Journal, No. 75, 160 (1985); and H. Nishimura, K. Kaku, T. Nakamura, Y. Fukazawa & J. Mizutani, Agric. Biol. Chem., 46, 319 (1982)). The p-menthane-3,8-diol involves structural isomers and optical isomers, namely, (+)-cis-p-menthane-3,8-diol, (-)-cis-p-menthane-3,8-diol, (+)-trans-p-menthane-3,8-diol and (-)-trans-p-menthane-3,8-diol. Each substance has a melting point ranging from 57 to 60.degree. C. It is in the form of a solid at room temperature but has a volatility in this state. Thus, it can exert the repellent effect on insect pests under certain atmosphere. When p-menthane-3,8-diol is not blended with a base but used as such, however, it exhibits volatility even in the form of a solid at room temperature, as described above, and the volatilization rate thereof cannot be controlled, which brings about serious waste.
In contrast thereto, JP-A-60-199804 (the term "JP-A" as used herein means a "published unexamined Japanese patent application") describes "A collar to which a resin impregnated with a repellent such as p-menthane-3,8-diol (PM) is used for pet such as dog". However, no particular resin is not specified therein. The addition of PM to resins, other than some limited ones, would be useless because of the following facts: (1) the added PM bleeds out onto the surface of the resin, which makes it impossible to control the volatilization rate thereof; or (2) the added PM is enclosed within the resin and can hardly volatilize.
When p-menthane-3,8-diol is added to a base resin comprising a single homopolymer, it is impossible to slowly volatilize and release the p-menthane-3,8-diol within an effective range from the surface of the base resin for a prolonged period of time, namely, so-called controlled release. The reason is as follows.
When a volatile substance is uniformly contained in a base material, the volatile substance present on the surface of the base material would volatilize into the atmosphere depending on its inherent vapor pressure. As a result, the concentration of the volatile substance on the surface of the base material differs from that at the core part, thus forming a concentration gradient. Then, the volatile substance present at the core part would slowly migrate into the surface layer and then volatilize into the atmosphere. Thus, the volatile substance within the base material would continuously volatilize into the atmosphere while maintaining the above flow. In order to slowly release a volatile substance in an appropriate amount for a prolonged period of time, therefore, it is required that the volatile substance is uniformly contained in a base material at a concentration allowing the formation of a continuous layer thereof; and that the migration rate of the volatile substance in the base material is controlled in such a manner that the volatile substance can volatilize at an appropriate volatilization rate.
The affinity of the base material for the volatile substance closely relates to the concentration and migration rate of the volatile substance. Thus, it is difficult to slowly release the volatile substance in an appropriate amount unless the affinity is appropriately controlled. When the affinity is excessively low, the compatibility between these substances becomes low. Thus, the volatile substance can be added to the base material only in a small amount. In this case, therefore, it is difficult to slowly release an appropriate amount of the volatile substance for a long time. When the affinity is excessively high, on the other hand, the high compatibility between these substances makes the migration rate of the volatile substance in the base material extremely low. In this case, therefore, it is difficult to volatilize an appropriate amount of the volatile substance.
When the base resin to which PM is to be added is a homopolymer, it is impossible to appropriately control the affinity of the base resin for PM, which causes the following problems. When the affinity of the homopolymer for PM is low, PM can be added only in a small amount. Thus, it is difficult to control the repellent effect of PM for a long time. When the affinity of the homopolymer for PM is high, on the other hand, the migration rate of PM becomes extremely low. Thus, it is difficult in this case to release PM in a satisfactory amount for achieving the aimed repellent effect.